The Pathology Center is acting as the coordinating center for this study. It is responsible for the standardization of the reporting of the pathologic material. It is standardizing the method of examination of the specimens both grossly and microscopically. It is collecting this material from the participating institutions and is preparing it for study. It is primarily concerned with the study of large bowel tumors and the effects of the irradiation on these tumors and on normal tissue. The findings are being analyzed in considerable detail and this information will be placed on IBM punch cards in order to tabulate the findings. Follow-up of the pathologic material particularly the autopsy and the acquiring of this new material and its processing is needed to accurately correlate our pathologic findings. At the end of this period information will be available as to the value of preoperative irradiation in carcinoma of the rectum.